Machine vision systems providing some degree of functionality related to inspecting the structure integrity of visibly clear glass and/or plastic containers have been conceived and constructed. Generally, such systems are based on the operation of an area array sensor, most typically a CCD sensor, sensitive to energy in the visible portion of the electromagnetic spectrum (400 nm to 700 nm). For purposes of this disclosure, the term visibly clear specifically means that the material allows very high optical transmission of electromagnetic radiation (light) falling within the 400 nm to 700 nm visible wavelength range.
One fairly obvious but important fact associated with objects manufactured from visibly clear material is that it is difficult, using state-of-the-art machine vision techniques, to inspect such objects for the presence of material voids in their final formed structure. This is significant because material voids such as holes or cracks are critical part defects which compromise the intended function of the product.
Machine vision, inspection systems typically operate by measuring the spatial variations of visible light as it reflects off or transmits through the structure. Since the objects which are to be inspected by such state-of-the-art systems are predominately clear in nature, the spatial light intensity variations which result from the presence of material voids in the material structure are quite small and result in less than adequate overall system performance. Stated in other words, holes and cracks in visibly clear objects are hard to see using machine vision systems operating within the visible region of the electromagnetic spectrum.
Another attribute of current state-of-the-art inspection systems is that they require a great deal of special purpose hardware and software in order to provide any level of product inspection. Light sources, imaging optics, cameras, control electronics, and an image processing computer executing custom inspection algorithms are required for baseline system functionality. This collection of hardware and software components result in an expensive inspection solution which, in many structural inspection applications, falls short of desired performance requirements.
The subject invention overcomes the problems of limited inspection performance and high cost by providing a sensor system operating at infrared wavelengths wherein the object under inspection is naturally opaque.